echoleaf on "[Plugin: Autoptimize] Internal error on 2nd install in cpanel"

I have Autoptimize installed on the first site in my Cpanel and it works fine.

I've made a copy of the site to a subdomain in the same cpanel, turned off all performance-oriented plugins, commented out define("WP_CACHE", true); in wp-config and edited the .htaccess file to the default WordPress version. I get the 500 internal server whenever turning on CSS.

Clearly the server is not the issue. Did I overlook something in the site config?

https://wordpress.org/plugins/autoptimize/